Pre-compensated optical tape wobble patterns

ABSTRACT

Amplitude or phase modulated un-compensated wobble patterns representing address patterns for track addresses of optical media are generated. A filter is applied to the un-compensated wobble patterns to pre-compensate the un-compensated wobble patterns. When an inverse of the filter is applied to a signal representing the pre-compensated wobble patterns in the presence of noise, the noise is suppressed and the un-compensated wobble patterns are substantially recovered.

TECHNICAL FIELD

This disclosure relates to optical tape and the encoding of informationthereon and decoding of information therefrom in the presence of noise.

BACKGROUND

Preformatting an optical media with wobbled edge land and groove tracksis an effective method for embedding recording track addresses on themedia. Wobble pattern blocks are normally a sequence of frequency,amplitude or phase modulated sine waves and are utilized as buildingblocks for a complete address field of the media recording tracks. Theseaddress fields usually include an index subfield (IF), a timing recoverysubfield (TRF) and an address bits subfield (AF).

SUMMARY

A method for encoding data on an optical media includes generatingun-compensated wobble patterns representing address patterns for trackaddresses of the optical media and applying a filter to theun-compensated wobble patterns to generate pre-compensated wobblepatterns such that when an inverse of the filter is applied to a signalrepresenting the pre-compensated wobble patterns in the presence ofnoise, the noise is suppressed and the un-compensated wobble patternsare substantially recovered. The method further includes embossing thepre-compensated wobble patterns on the optical media.

An optical media encoding system includes an encoder that generatesun-compensated wobble patterns representing address patterns for trackaddresses of an optical media and applies a filter to the un-compensatedwobble patterns to generate pre-compensated wobble patterns such thatwhen an inverse of the filter is applied to a signal representing thepre-compensated wobble patterns in the presence of noise, the noise issuppressed and the un-compensated wobble patterns are substantiallyrecovered.

A computer-readable medium has instructions stored thereon that, whenexecuted by a computer, cause the computer to generate un-compensatedwobble patterns representing address patterns for track addresses of anoptical media and to apply a filter to the un-compensated wobblepatterns to generate pre-compensated wobble patterns such that when aninverse of the filter is applied to a signal representing thepre-compensated wobble patterns in the presence of noise, the noise issuppressed and the un-compensated wobble patterns are substantiallyrecovered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an index block waveform.

FIG. 2 shows an address bit block waveform.

FIG. 3 shows a timing recovery block waveform.

FIG. 4 shows an address pattern waveform including the blocks of FIGS. 1through 3.

FIG. 5 is a block diagram of a track address decoder.

FIG. 6 shows a wobble pattern waveform (without noise) added to adelayed version of itself, and the resulting index pattern waveform.

FIG. 7 shows a wobble pattern waveform (without noise) and resultingindex pattern waveform.

FIG. 8 shows an un-filtered wobble pattern waveform (with noise) andresulting index pattern waveform.

FIG. 9 shows a filtered wobble pattern waveform and resulting indexpattern waveform.

FIGS. 10 and 11 are block diagrams of signal processing systems.

FIGS. 12 and 13 show waveform output, without and with noiserespectively, from a wobble format pattern generator.

FIG. 14 shows a waveform output of a band pass filter.

FIG. 15 shows a waveform for an index pattern in a 2 cycle tape format.

FIG. 16 shows a waveform for a ‘1’ bit in the 2 cycle tape format.

FIG. 17 shows a waveform for an address in the 2 cycle tape format.

FIG. 18 shows the application of a matched filter tuned to the indexpattern of FIG. 15.

FIG. 19 shows the result of the application of the matched filter ofFIG. 18.

FIG. 20 shows the application of a matched filter tuned to the ‘1’ bitpattern of FIG. 16.

FIG. 21 shows timing requirements to confirm an index.

FIG. 22 shows a waveform having an index, three ‘1’ bits, and addressbits.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. As those of ordinary skill in the art will understand,various features illustrated and described with reference to any one ofthe figures can be combined with features illustrated in one or moreother figures to produce embodiments that are not explicitly illustratedor described. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

Referring to FIGS. 1 through 4, dual cycle wobble block patterns, suchas the index block of FIG. 1, the address bit block of FIG. 2, and thetiming recovery block of FIG. 3, have been implemented as examplefoundational elements of an address field pattern, such as the patternof FIG. 4, for optical tape media. Phase modulated dual cycle blocks, inthis example, represent the index or sync field (IF), a set of monotonecycle fields (TRF) around the index fields can be used for timingrecovery of the decoder, and the eight subsequent pairs of cyclesrepresent the 8 bits of the address field (AF).

Referring to FIGS. 5 and 6, a track address decoder 10 may include adelay filter 12, threshold detector 18, phase lock loop (PLL) 20,synchronizer 22, synchronized rectifier 24, synchronized resettableintegrator 26 and threshold detector 28. The delay filter 12 may includea delay block 14 and sum block 16. A wobble pattern, such as the wobblepattern of FIG. 6, can be input to the delay block 14 and sum block 16.The resulting output of the delay block 14, such as the delay pattern ofFIG. 6, can also be input to the sum block 16. The resulting output ofthe sum block 16, such as the index pattern of FIG. 6, can be input tothe threshold detector 18. An output of the threshold detector 18 andthe wobble pattern of FIG. 6 can be input to the phase lock loop 20. Theresulting output of the phase lock loop 20 can be input to thesynchronizer 22. An output of the synchronizer 22 and the wobble patternof FIG. 6 can be input to the synchronized rectifier 24. The resultingoutput of the synchronized rectifier 24 and the wobble pattern of FIG. 6can be input to the synchronized resettable integrator 26. The resultingoutput of the synchronized resettable integrator 26 can be input to thethreshold detector 28. In this arrangement, an output of the thresholddetector 28 yields the address associated with the wobble pattern.

The delay filter or buffer 12 generates a half cycle delayed patternrelative to the original wobble pattern. Adding the two patterns at thesum block 16 yields a detectable sync half cycle (index) that can bedetected by the threshold comparator 18 when a peak value of the indexpattern exceeds the index threshold. Once detected, the phase lock loop20, locked to the monotone pattern of the timing recovery subfieldsdiscussed with reference to FIG. 4, establishes the timing of each bitof the address subfield and the address is decoded via the synchronizer22, synchronized rectifier 24, synchronized resettable integrator 26 andthreshold detector 28 as known in the art.

A robust and efficient track address coding/decoding scheme may beuseful to a reliable data recoding and retrieval process as wobblepatterns in optical recording systems can be susceptible to media noiseand pre-formatting process imperfections. This susceptibility is due tothe fact that the amplitude of physical wobble nanostructures isrelatively small compared to the land and groove structures, which iscaused by limitations imposed by read/write channel Inter-SymbolInterference. Hence, disclosed herein are wobble coding,pre-compensating and decoding technologies that can improve, in certainexamples, effective signal-to-noise ratio (SNR) of wobble signalpatterns.

Pre-Compensated Wobble Patterns

Referring to FIGS. 7 and 8 respectively, example decoder performance isexamined without and with noise in the channel. Under excessive noise,the reliability of decoder functionality may be compromised as thedecoder may be unable to distinguish between data embedded in the signaland noise associated with the signal. Peak values of the index pattern(with noise) that do not correspond with an index field of the wobblepattern (with noise), for example, may exceed the index threshold. Thismay lead the decoder to falsely detect an index field. Likewise, peakvalues of the index pattern (with noise) that correspond with an indexfield of the wobble pattern (with noise), for example, may not exceedthe index threshold. This may lead the decoder to not detect an indexfield.

Referring to FIG. 9, index pattern SNR can be improved by applying anarrow band pass (BP) filter to the wobble signal centered at patterncarrier frequency. Because the wobble signal is amplitude and phasemodulated, however, the application of a narrow BP filter can change theshape of the patterns and thus impact the performance of the decoder.That is, the decoder may be unable to decode the filtered index signalbecause, for example, peak values of the filtered index that exceed theindex threshold signal may no longer correspond to address index blocks.

Certain pre-compensating strategies can apply an inverse filter (e.g.,an inverse BP filter centered at the carrier frequency, an inverse lowpass (LP) filter having a corner frequency at the carrier frequency,etc.) to wobble patterns prior to imprinting (formatting) of the media.The imprinted wobble patterns on the media are pre-compensated such thatdecoder filtering (e.g., BP filtering, LP filtering, etc.) of the readback wobble pattern yields (substantially) the original signal shape atan output of the filter.

Referring to FIG. 10, a traditional signal processing block diagramincludes a media pre-formatting process 30 and drive address decodingprocess 32 for an optical media 34. During the pre-formatting process30, track address information 36 is input to a wobble format patterngenerator 38 to pre-format the optical media 34. During the driveaddress decoding process 32, an optical pickup unit 40 reads data fromthe optical media 34. The data then is input to a wobble patterndetector 42 and track address decoder 44 as known in the art. Asmentioned above however, the drive address decoding process 32 may behampered by excessive noise associated with the signal.

Referring to FIG. 11, an example of an improved signal processing blockdiagram includes a media pre-formatting process 46 and drive addressdecoding process 48 for an optical media 50. During the pre-formattingprocess 46, track address information 52 is input to a wobble formatpattern generator 54, which generates, in certain examples, amplitudeand phase modulated un-compensated wobble patterns representing addresspatterns for track addresses of the optical media 50. An inverse BPfilter 56 is applied to pre-compensate the un-compensated wobblepatterns. The pre-compensated wobble patterns are then embossed on theoptical media 50.

During the drive address decoding process 48, an optical pickup unit 58reads data from the optical media 50. The data is then input to a wobblepattern detector 60, a BP filter 62 and track address decoder 64.Application of the BP filter 62, however, does not change the shape ofthe wobble patterns in such a way so as to make them unrecognizable tothe track address decoder 64 because the inverse BP filter 56pre-compensated the wobble patterns to account for shape alteringeffects associated with the application of the BP filter 62.

Referring to FIGS. 12 and 13 respectively, example output without andwith noise in the channel from the wobble format pattern generator 54(original wobble pattern signal) and inverse BP filter 56(pre-compensated wobble pattern signal) is illustrated. As discussedabove, application of the BP filter 56 prior to embossing on the opticalmedia 50 alters the waveform of the wobble patterns such that afterapplication of the BP filter 62 during the drive address decodingprocess 48, the wobble patterns can be decoded by the track addressdecoder 64.

Referring to FIG. 14, example output from the BP filter 62 (filteredwobble pattern) is illustrated along with the index pattern that resultsfrom adding a delayed version to itself as discussed with reference toFIG. 5. BP filtering suppresses noise and substantially yields theoriginal wobble address pattern. As mentioned above, this signal is theninput to the track address decoder 64, which operates much like thetrack address decoder 10 of FIG. 5. The index decoder of the trackaddress decoder is thus able to detect the sync field of the indexwobble pattern by detecting index wobble pattern peak values above athreshold even though noise was in the channel because there is littlechange to cycle pattern shape of the original wobble signal. That is,peak values greater than the index threshold still correspond to addressindex blocks of the decoded wobble pattern.

Matched Filter Based Optical Tape Decoding

Referring to FIGS. 15 though 17, track addresses in certain tape formatscan be coded in wobble as a series of sine waves as mentioned above.Blocks of address bits are delineated by index patterns, such as theindex pattern of FIG. 15. The addresses are encoded as gray-coded valueswith the presence of a multi-cycle (e.g., dual cycle) sine wave, such asthe ‘1’ bit waveform of FIG. 16, representing a ‘1’ bit and the absenceof such representing a ‘0’ bit. Rapid and reliable address decoding forthe address pattern of FIG. 17, which includes the waveforms of FIGS. 15and 16, in the presence of tracking noise, for example, can facilitatetimely reading and writing of data. Technology described herein candecode addresses using a matched filter approach for index and bitdetection. These matched filters, in certain circumstances, can beadvantageous because of their ability to reject out-of band signalnoise.

In one example, track address information can be decoded using twodifferent matched filters: one having coefficients representing theindex waveform of FIG. 15 and another having coefficients representingthe ‘1’ bit waveform of FIG. 16. Referring to FIG. 18, an index encodedwithin an address waveform, such as the address waveform of FIG. 17, canbe detected by applying a matched filter 66 including a multiplier 68and integrator 70 and tuned to the dual cycle waveform of FIG. 15according toRi(T)=Σ_(x=0) ³³ l((T+1)*33−x)*A(33*T+x)  Equation 1where Ri(T) is the output of the filter 66 and T is the sample time ofthe decoder (T=0, 1, 2, 3, . . . ). That is, the filter output, Ri(T),is the convolution of the index waveform, l(n), and the addresswaveform, A(n). Put a different way, a prototype dual cycle index signalpattern 72 similar to that illustrated in FIG. 15 can be input to themultiplier 68 along with an address pattern 74 similar to thatillustrated in FIG. 17; output of the multiplier 68 is then input to theintegrator 70.

Referring to FIG. 19, output of the integrator 70 is illustrated. Indexdetection occurs when a peak signal value exceeds a predeterminedthreshold. This threshold can be determined for each coding schemethrough, for example, experimentation, etc. The address decoder firstsearches for an index. Once detected, it then switches modes andsearches for a predetermined pattern of bits to confirm a location ofthe index.

Referring to FIG. 20, a ‘1’ bit can be detected by applying a matchedfilter 76 including a multiplier 78 and integrator 80 and tuned to the‘1’ bit waveform of FIG. 16 according toRa(T)=Σ_(x=0) ³³α((T+1)*33−x)*A(33*T+x)  Equation 2where Ra(T) is the output of the filter 76 and T is the sample time ofthe decoder (T=0, 1, 2, 3, . . . ). That is, the filter output, Ra(T),is the convolution of the ‘1’ bit waveform, a(n), and the addresswaveform, A(n). Put a different way, a prototype ‘1’ bit signal pattern82 similar to that illustrated in FIG. 16 can be input to the multiplier78 along with an address pattern 84 similar to that illustrated in FIG.17; output of the multiplier 78 is then input to the integrator 80.

Referring to FIG. 21, output of the integrator 80 is shown. Certainaddress formats place three ‘1’ bits at a pre-determined time after theindex waveform. The index can be confirmed by detecting these three ‘1’bits. ‘1’ bits are detected based on the result of a matched filtertuned to the ‘1’ bit of FIG. 16. To be valid, these ‘1’ bits should havecorrect amplitude and timing from the index. Once the index has beenconfirmed, address bits are detected by searching for peaks in thematched filter response to the ‘1’ bit of FIG. 16. ‘1’ bits areconfirmed by amplitude and timing from the most recently detected ‘1’bit. For address detection, a quality of the bit is also assigned. Thisquality provides an indication of the likelihood of the bit having beenmis-detected.

Referring to FIG. 22, a fully decoded address from the signal of FIG. 17is illustrated. A high quality (HQ) ‘1’ bit is detected if the peak inthe ‘1’ bit tuned matched filter output is above a pre-determinedthreshold and is at the expected time after the last ‘1’ bit detection.An HQ ‘0’ bit is detected if the peak is below a differentpre-determined threshold. Low quality bits are detected if the peak isbetween these two thresholds. A low quality (LQ) ‘1’ bit is detected ifthe peak is below the HQ ‘1’ bit threshold but above an intermediatethreshold (LQ threshold). A low quality ‘0’ bit is detected if the peakis below the intermediate threshold but above the HQ ‘0’ bit threshold.These threshold values can be determined for each coding scheme through,for example, experimentation, etc.

In the example of FIG. 22, the index is confirmed by three ‘1’ bits(monotone) with the correct timing from the index. The address, in thisexample [1 1 0 0 0 1 0 1], is then detected. All 8 address bits happento be of high quality. This same approach can be used to decodeaddresses coded with tri cycle or other patterns.

The processes, methods, or algorithms disclosed herein can bedeliverable to/implemented by a processing device, controller, orcomputer, which can include any existing programmable electronic controlunit or dedicated electronic control unit. Similarly, the processes,methods, or algorithms can be stored as data and instructions executableby a controller or computer in many non-transitory forms includinginformation permanently stored on non-writable storage media such as ROMdevices and information alterably stored on writeable storage media suchas floppy disks, magnetic tapes, CDs, RAM devices, and other magneticand optical media. The processes, methods, or algorithms can also beimplemented in a software executable object. Alternatively, theprocesses, methods, or algorithms can be embodied in whole or in partusing suitable hardware components, such as Application SpecificIntegrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs),state machines, controllers or other hardware components or devices, ora combination of hardware, software and firmware components.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes mayinclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, embodimentsdescribed as less desirable than other embodiments or prior artimplementations with respect to one or more characteristics are notoutside the scope of the disclosure and can be desirable for particularapplications.

What is claimed is:
 1. A method for encoding data on an optical mediacomprising: generating un-compensated wobble patterns representingaddress patterns for track addresses of the optical media; applying afilter to the un-compensated wobble patterns to generate pre-compensatedwobble patterns such that when an inverse of the filter is applied to asignal representing the pre-compensated wobble patterns in the presenceof noise, the noise is suppressed and the un-compensated wobble patternsare substantially recovered; and embossing the pre-compensated wobblepatterns on the optical media.
 2. The method of claim 1, wherein thewobble patterns have a carrier frequency and wherein the filter is aninverse band-pass filter centered at the carrier frequency.
 3. Themethod of claim 1, wherein the wobble patterns have a carrier frequencyand wherein the filter is an inverse low-pass filter having a cornerfrequency at the carrier frequency.
 4. The method of claim 1, whereinthe wobble patterns include dual cycle phase shifted wobblesrepresenting address index sub-fields.
 5. The method of claim 1, whereinthe wobble patterns include dual cycle wobbles representing address bitssub-fields.
 6. The method of claim 1, wherein the wobble patternsinclude multi-cycle wobbles representing timing recovery sub-fields. 7.An optical media encoding system comprising: an encoder configured togenerate un-compensated wobble patterns representing address patternsfor track addresses of an optical media and to apply a filter to theun-compensated wobble patterns to generate pre-compensated wobblepatterns such that when an inverse of the filter is applied to a signalrepresenting the pre-compensated wobble patterns in the presence ofnoise, the noise is suppressed and the un-compensated wobble patternsare substantially recovered.
 8. The system of claim 7, wherein thewobble patterns have a carrier frequency and wherein the filter is aninverse band-pass filter centered at the carrier frequency.
 9. Thesystem of claim 7, wherein the wobble patterns have a carrier frequencyand wherein the filter is an inverse low-pass filter having a cornerfrequency at the carrier frequency.
 10. The system of claim 7, whereinthe wobble patterns include dual cycle phase shifted wobblesrepresenting address index sub-fields.
 11. The system of claim 7,wherein the wobble patterns include dual cycle wobbles representingaddress bits sub-fields.
 12. The system of claim 7, wherein the wobblepatterns include multi-cycle wobbles representing timing recoverysub-fields.
 13. A non-transitory computer-readable medium havinginstructions stored thereon that, when executed by a computer, cause thecomputer to (i) generate un-compensated wobble patterns representingaddress patterns for track addresses of an optical media and (ii) applya filter to the un-compensated wobble patterns to generatepre-compensated wobble patterns such that when an inverse of the filteris applied to a signal representing the pre-compensated wobble patternsin the presence of noise, the noise is suppressed and the un-compensatedwobble patterns are substantially recovered.
 14. The medium of claim 13,wherein the wobble patterns have a carrier frequency and wherein thefilter is an inverse band-pass filter centered at the carrier frequency.15. The medium of claim 13, wherein the wobble patterns have a carrierfrequency and wherein the filter is an inverse low-pass filter having acorner frequency at the carrier frequency.
 16. The medium of claim 13,wherein the wobble patterns include dual cycle phase shifted wobblesrepresenting address index sub-fields.
 17. The medium of claim 13,wherein the wobble patterns include dual cycle wobbles representingaddress bits sub-fields.
 18. The medium of claim 13, wherein the wobblepatterns include multi-cycle wobbles representing timing recoverysub-fields.